1. Field of the Invention
Embodiments of the invention relate to methods and systems for producing valuable chemicals, such as alternative liquid fuels. Specific embodiments involve methods and systems for producing valuable chemicals that include the conversion of hydrocarbon-containing materials into valuable chemicals by subjecting at least a portion of the hydrocarbon-containing material to gasification/partial oxidation to produce synthesis gas (“syngas”), the syngas containing primarily carbon monoxide (CO) and hydrogen (H2). The method and system also includes introducing at least an alcohol (in which the alcohol may be generated or otherwise derived through fermentation of a hydrocarbon-containing material) and the syngas to a reformer to generate saturated hydrocarbons, higher alcohols, or combinations thereof. The system includes the unit operations and process streams useful in carrying out the method.
2. Description of the Related Art
Alternative liquid transportation fuels could provide economic, security, and environmental benefits. Increased worldwide energy demands from countries such as India and China are likely to increase oil and fuel prices and may lead to new political conflicts. Further, carbon-based greenhouse gas emissions continue to accumulate in the atmosphere, and the industrialization of those populous countries likely will accelerate that accumulation. Transportation fuels derived from locally available inputs could reduce, or slow the growth in, demand for crude oil and help to mitigate these problems.
Transportation fuels derived from renewable biomass, or “biofuels,” are of particular commercial interest. Biomass can be viewed as intermediate-term storage of solar energy and atmospheric carbon, via photosynthesis and carbon fixing mechanisms. With cultivation and harvesting cycles measured in months, biomass is, in principle, a renewable domestic energy resource.
The two most developed and commercially available, non-petroleum-based alternative fuels are biodiesel and bioethanol. For automotive transportation fuels, “bioethanol,” or ethanol derived from biological sources, is the commercial leader. However, bioethanol's chemical and physical property deficiencies relative to conventional combustion fuels such as gasoline limit its attractiveness as a fuel. The volumetric energy density of ethanol is approximately 70% of typical unleaded gasoline products. In addition, the volatility and fugitive loss potential of ethanol is considerably higher. Carbohydrates such as sugars and simple starches are the biomass components most easily converted into ethanol. Corn, wheat, and sugar cane are the most commonly used crops and their use impacts food prices and availability. Finally, most automobiles have not been modified to run on bioethanol as a stand-alone fuel. Thus, bioethanol's use is currently limited to a low-percentage gasoline additive.
Simple alcohols can be manufactured through several processes. Methanol, for example, is commonly produced using natural gas reforming reactions; petroleum feedstocks also can be converted and reformed. Propanol and higher alcohols typically are produced from petrochemical sources, although some bioprocessing options are also becoming more viable. For ethanol, fermentation of sugars, either directly from sugar plants such as cane and beet, or indirectly, from sugars derived by saccharification of other carbohydrates such as corn grain and wheat grain is well-established and popular. The latter route, starting with corn, is the most common approach in the United States.
Fermentation science dates back eight millennia (“8,000-year-old Wine Unearthed in Georgia”; London, UK, Dec. 28, 2003 (author unknown)) and has long been practiced with only incremental improvements. While the scale of bioethanol facilities has increased (i.e., facilities now commonly have capacities of 100M gallons per year (gpy) in the US and more than 200M gpy in China), the basic chemical and biological processes remain the same. See Berg, C., “World Fuel Ethanol Analysis and Outlook”, archived at http://www.distill.com/World-Fuel-Ethanol-A&O-2004.html (2004).
The long-standing limitations of fermentation from grain are well understood. These include: (i) energy intensity of the process; (ii) high water usage or water treatment burden; (iii) maximum theoretical utility of only 51% of the carbohydrate substrate, none from cellulose; (iv) economics dependent on a primary co-product of regional and seasonal value often called distiller's grains and solubles (“DGS”); if dried, dried distiller's grains and solubles (“DDGS”); and (v) consumption of valuable, food-chain capable, carbohydrate resources.
State-of-the-art fermentation processes yield a relatively dilute intermediate of typically 7-15% ethanol in water, along with a number of other byproducts. Energy-intensive distillation usually is required to concentrate and further purify the ethanol. In addition, physical separation approaches, such as phase separation and/or azeotropic distillation, are often used to overcome the well-known azeotrope between water and ethanol, which otherwise resists separation by simple distillation. As a result, the energy payback ratio, or the energy value of a product relative to the required process energy inputs, is typically close to, or even less than, break-even. Pimentel, D., “Ethanol Fuels: Energy Balance, Economics, and Environmental Impacts are Negative”, Natural Resources Research, 12, vol. 2, 127-134 (2003).
It is hypothesized that a heavier range of chemicals, including both hydrocarbons and simple (mono) alcohols, might offer superior performance as fuel components, and greater chemical value in other applications. Significant biofuels research and development efforts therefore are being devoted to this hypothesis. For example, DuPont and BP have announced the pursuit of biological routes to butanol, or “biobutanol”, as a preferred fuel supplement. Superior fuel performance of butanol relative to ethanol has been quantitatively supported by fuel property testing results. See BP Corporation Press Release, “Test Results Show Biobutanol Performs Similarly to Unleaded Gasoline”, BP Corporation Press Release, Apr. 20, 2007; archived via Green Car Congress website: http://www.greencarcongress.com/2007/04/test_results_sh.html#more.
Even heavier alcohols (i.e., those heavier than butanol), and analogous hydrocarbons may be even more valuable as fuel replacements. Thus, mixtures of aliphatic hydrocarbons and some higher alcohol and/or ether species may be a more desirable synthetic fuel mixture for today's automotive engines. The advantages of such fuel mixtures have also been disclosed by Jimeson et al. (Standard Alcohol Company of America). Jimeson, R. M., Radosevich, M. C., and Stevens, R. R., “Mixed Alcohol Fuels for Internal Combustion Engines, Furnaces, Boilers, Kilns and Gasifiers,” International Application under the Patent Cooperation Treaty (PCT), WO 2006/088462 A1; PCT Publ. Date Aug. 24, 2006, the disclosure of which is incorporated by reference herein in its entirety.
Beretta et al. also recognized a need to shift the fuel product MWD to higher species, and proposed a multi-step approach via dual-bed operations and further downstream processing. See Beretta, A., Qun Sun, R. B. Herman, and K. Klier, “Production of Methanol and Isobutyl Alcohol Mixtures over Cesium-Promoted Cu/ZnO/Cr2O3 and ZnO/Cr2O3 Catalysts”, Ind. Eng. Chem. Res., 35; 1534-1542 (1996).
The creation of the first C—C bond, the central bond in ethanol, is energetically the most difficult hurdle in these synthetic chemical pathways. Bell et al. acknowledged this limitation in alcohol synthesis from syngas, and taught a method of building up higher weight species via methanol synthesis, followed by continuous recycle with homologation. Bell, P. S., L. W. Bolton, B. P. Gracey, and M. K. Lee, “Process for the Conversion of Synthesis Gas to Oxygenates Containing C2+ Alcohols”, International Application under the Patent Cooperation Treaty (PCT), WO 2007/003909 A1; PCT Publ. Date Jan. 11, 2007, the disclosure of which is incorporated by reference herein in its entirety. Due to recompression in each recycle pass, this method is somewhat energy intensive and yields a substantial portion of residual methanol and an undesirable byproduct ester.
Gasification, a form of partial oxidation of feedstocks to yield a high value energy or chemical intermediate gas mixture, is one well-established approach to deriving energy values from solid hydrocarbons. Most of the existing technology base in gasification was developed for coal conversion. Coal gasification, using the integrated gasification/combined cycle (IGCC) approach, is a mature commercial technology in which coal is first converted into synthesis gas (“syngas”), a mixture primarily of carbon monoxide (CO) and hydrogen (H2). This energy conversion option has been well documented by many authors and inventors; notable is the recent review by Minchener. Minchener, A. J., “Coal Gasification for Advanced Power Generation,” Fuel, 84; 2222-2235 (2005). Extension of gasification technology to biomass feedstocks also has been well documented, for example by van Heek et al. van Heek, K. H., B. O. Strobel and W. Wanzl, “Coal Utilization Processes and their Application to Waste Recycling and Biomass Conversion,” Fuel, 73(7); 1135-1143 (1994).
The syngas mixture that results from gasification processes can be used as a synthetic chemicals feedstock or, on very large scales, further converted through full oxidation in a gas turbine and steam recovery system. This approach captures value from the electrical output and the steam which can be used directly, or further converted into additional electric power. Due to limitations in gasification reactor performance, however, carbon dioxide and undesirable tar and oil fragments are common in the syngas mixture, as is the partial generation of methane (CH4). Accordingly, available carbon is underutilized, and potential greenhouse gas (GHG) reductions are not realized. In addition, operational difficulties such as fouling and plugging occur, and the potential for emissions of hazardous trace gas pollutants increases.
For several decades, entrained flow gasifiers, particularly those of the high-temperature (>1200° C.) slagging type, have predominated gasification designs. Reactors with more homogeneous composition and temperature fields, most notably the fluidized bed gasification system, however, have been used and documented extensively in recent years. See, e.g., Selinger et al., “TwinRec Gasification and Ash Melting Technology—Now Established for Municipal Waste,” 4th International Symposium on Waste Treatment Technologies, Sheffield, UK (2003). The fluidized bed operates at lower average gasification temperatures (typically <1100° C.), reducing energy losses and increasing containment system lifetimes. It also has the potential for greater operational stability and robustness of process control, with respect to both physical and chemical forms and variances in the incoming feed.
Molten metal gasification technology, which has been used largely for waste conversion, offers benefits similar to those offered by the fluidized bed, such as increased control and stability. Its potential for biomass or other hydrocarbon conversion for advanced energy applications also is established in the patent literature. For example, McGeever and Nagel describe partial oxidation of hydrocarbons via a molten metal gasification system, yielding syngas which can be further transformed, as described previously. McGeever, C. E. and C. J. Nagel, “Method and System of Formation and Oxidation of Dissolved Atomic Constituents in a Molten Bath,” U.S. Pat. No. 5,866,095, the disclosure of which is incorporated by reference herein in its entirety.
The importance and potential of the Fischer-Tropsch (“F-T”) and related syntheses for alcohol derivation from biomass, including current industrial efforts to pursue these routes commercially, are detailed in the comprehensive review of Spath and Dayton of the National Renewable Energy Laboratory (NREL). Spath, P. L. and D. C. Dayton, Preliminary Screening—Technical and Economic Assessment of Synthesis Gas to Fuels and Chemicals with Emphasis on the Potential for Biomass-Derived Syngas; NREL/TP-510-34929, December 2003. A wide number of pathways are available, and many of these can be summarized in broad mechanistic groupings.
Reformation of syngas to aliphatic liquid hydrocarbons (suitable for various fuel applications), for example, was first pioneered by Fischer and Tropsch nearly a century ago. While this chemistry has been commercially practiced for decades, most notably by SASOL (South Africa), the coal-to-liquids approach has not held universal economic appeal. A review of the status and history of the Fischer-Tropsch synthesis (and related syntheses), as well as its place among similar or competing coal conversion strategies, was provided by Schobert and Song. Schobert, H. H. and C. Song, “Chemicals and Materials from Coal in the 21st Century,” Fuel, 81; 15-32 (2002).
Fischer-Tropsch catalysts and process schemes have a propensity to yield an exponential, Flory-Shultz product distribution, which includes a substantial fraction of lighter species, particularly methane. Paul, Ratnasamy (2007) F-T proposal submitted to the National Centre of Catalysis Research (NCCR—India). NCCR Internal Bulletin (unpublished); archived at: http://203.199.213.48/1089/. Similarly, in alcohol production via syngas homologation, methanol (CH3OH) is the primary product, unless significant and energy-intensive intermediate recycle is used. Since methanol, similar to ethanol, has physical property shortcomings relative to gasoline, the use of this route to generate these chemicals has been limited.
“Higher alcohols,” those heavier than methanol or “C2+” alcohols, also can be accessed by catalytic mechanisms that are similar to and derived from the Fischer-Tropsch route. One higher alcohol pathway that has been investigated is “aldol coupling with oxygen retention reversal”, documented by Nunan et al., among others. Nunan, J. G., R. G. Herman and K. Klier, “Higher Alcohol and Oxygenate Synthesis over Cs/Cu/ZnO/M2O3 (M═Al, Cr) Catalysts,” Journal of Catalysis, 116; 222-229 (1989). In this route higher alcohols are generated via chain growth of smaller, primary alcohols, through condensation with dehydration. The analogous condensation reaction between methanol and ethanol is also of interest because of established routes to each reactant from biomass. This is described as the Guerbet Reaction pathway, yielding propanol and heavier alcohols through the “Higher Alcohol Biorefinery” concept of Olson et al. Olson, E. S., R. K. Sharma and T. R. Aulich, “Higher Alcohols Biorefinery—Improvement of Catalyst for Ethanol Conversion,” Applied Biochemistry and Biotechnology, 115; 913-932 (2004).
Interest in generation of oxygenated hydrocarbon chemicals, most notably as fuel components, was pursued by Gheysens et al. in the post-F-T synthesis of light ethers. Gheysens, J.-L. G. et al., “Composition and method for producing a multiple boiling point ether gasoline component,” U.S. Pat. No. 6,017,371; Jan. 25, 2000, the disclosure of which is incorporated by reference herein in its entirety. Analogous synthesis of light branched alcohols, or “isoalcohols”, was developed by Vanderspurt et al., in addition to the researchers cited earlier in this field. Vanderspurt, T. H. et al., “Isoalcohol synthesis”, U.S. Pat. No. 5,703,133; Dec. 30, 1997, the disclosure of which is incorporated by reference herein in its entirety. A wider range of possible feedstocks, including wastes, was applied by Fujimura et al. Fujimura, H. et al., “Method and apparatus for treating wastes by gasification”, U.S. Pat. No. 6,676,716; Jan. 13, 2004, the disclosure of which is incorporated by reference herein in its entirety.
Landis et al. described the pursuit of two product types in tandem, from F-T routes, broadly in terms of hydrocarbons and oxygenates. Landis, S. R. et al., “Managing hydrogen and carbon monoxide in a gas to liquid plant to control the H2/CO ratio in the Fischer-Tropsch reactor feed”, U.S. Pat. No. 6,872,753; Mar. 29, 2005, the disclosure of which is incorporated by reference herein in its entirety. Miller et al., and its precursors, taught the synthesis of higher alcohols from syngas over a mixed Cu—Cr oxide catalyst. Miller, J. T. et al., “Catalytic process for producing olefins or higher alcohols from synthesis gas,” U.S. Pat. No. 5,169,869; Apr. 28, 1992, the disclosure of which is incorporated by reference herein in its entirety. Earlier, Quarderer et al. described the use of “lower alcohols” and syngas to generate higher alcohols, specifically over a Mo-based catalyst, without specifying equipment or reaction engineering details. Quarderer, D. J. et al., “Preparation of ethanol and higher alcohols from lower carbon number alcohols”, U.S. Pat. No. 4,825,013; Apr. 25, 1989, the disclosure of which is incorporated by reference herein in its entirety.
Energy integration advantages were allegedly captured by Price in the form of electric power. Price, J. G., “Production of hydrocarbon products”, U.S. Pat. No. 6,673,845; Jan. 6, 2004, the disclosure of which is incorporated by reference herein in its entirety. Energy integration advantages also were allegedly realized by Arcuri et al. in the form of thermal energy integrated within FT hydrocarbon synthesis reactions. Arcuri, K. B. et al., “Structured Fischer-Tropsch catalyst system and method”, U.S. Pat. No. 6,797,243; Sep. 28, 2004, the disclosure of which is incorporated by reference herein in its entirety. Allison et al. pursued reactive distillation process simplification in the synthesis of methanol. Allison, J. D. et al., “Use of catalytic distillation reactor for methanol synthesis”, U.S. Pat. No. 6,723,886; Apr. 20, 2004, the disclosure of which is incorporated by reference herein in its entirety.
Upgrading of alcohols or other intermediates from bioprocesses might be accomplished in a variety of different heterogeneous reactor configurations. Gracey and Bolton have disclosed the use of reactive distillation in the synthesis of light olefins from alcohols. Gracey, B. P. and L. W. Bolton, “Reactive Distillation for the Dehydration of Mixed Alcohols”, International Application under the Patent Cooperation Treaty (PCT), WO 2007/003899 A1; PCT Publ. Date Jan. 11, 2007, the disclosure of which is incorporated by reference herein in its entirety.
An additional limitation of both existing fermentation processes, and high-temperature thermal processes, such as gasification, is that energy released during processing is not effectively captured or otherwise integrated to the process scheme. In particular, the separation, concentration and purification of ethanol from a dilute fermentation broth, is quite energy intensive—a factor which can greatly limit, or even eliminate, any net energy gain (“energy payback”) associated with bioethanol production. Pimentel, D., “Ethanol Fuels: Energy Balance, Economics, and Environmental Impacts are Negative”, Natural Resources Research, 12, vol. 2, 127-134 (2003).
In summary, there are several shortcomings associated with current processes to derive select chemicals, for example, liquid fuels from biomass or other abundant non-petroleum resources. Fermentation is practical only for ethanol production from grain-derived carbohydrates. It consumes significant energy, faces substantial challenges regarding water management, and converts less than half the available carbon into fuel. Additionally, ethanol has limited use as a chemical feedstock, as well as drawbacks (e.g., low energy density, high fugitive loss potential, and difficult phase behavior with water) when used as a fuel. Further, Fischer-Tropsch and related syntheses (the primary alternative routes to produce chemicals and fuels from these feedstocks) offer limited selectivity to desired chemical (or fuel) species, with challenges of control, in terms of heat removal and stability of the resulting product mix (e.g., molecular weight distribution).
The description herein of advantages or disadvantages of certain methods and systems is not intended to limit the various embodiments disclosed herein to either their inclusion or exclusion. Indeed, certain embodiments may include one or more known systems or methods, without suffering from the disadvantages described herein.